1. Field of the Invention
The present invention relates to new improved compositions and methods for dispersing hydrophilic water-soluble polymers in aqueous liquids.
It is well known in the art that high molecular weight hydrophilic water-soluble polymers are very difficult to disperse in aqueous liquids. In conventional processes for dissolving such polymers, dry powdered polymer is fed slowly and carefully into the vortex of a vigorously stirred body of water. However, it is frequently difficult to do this in actual operation for a number of reasons. The desired end result is to completely separate and wet each individual polymer particle so no agglomerated particles form, commonly called fish eyes. Mechanical feeders frequently fail and are less than 100% efficient. Sifting polymers by hand is a highly tedious procedure. Often, for example, personnel tend to simply dump the powder into the water, start up the stirrer and expect the material to dissolve. Under such circumstances, the polymers swell and ball up into extremely viscous masses with dry and unswollen material inside which the water cannot even reach to dissolve. Many undissolved, so-called "fish eyes," result. Fish eyes may not necessarily float. Fish eyes may sink to the bottom of the tank, depending upon the density of the fish eyes and the aqueous liquid. Under normal circumstances, depending on the particular water-soluble polymer, it is impossible to get such a mass to completely dissolve even after hours or even days of stirring. For this reason, a considerable amount of work has been done in an attempt to develop improved and useful methods for producing dispersions and solutions of high molecular weight, water-soluble polymers in water. Sometimes the dry powdered polymer is wetted with a water-soluble organic solvent or it may be wetted with a surface active material in an attempt to improve the penetration of liquid into the particles, at the same time acting to separate them. Considerable fractions of water-soluble inert salts, such as sodium chloride or effervescing salts, may be used in order to separate the particles of polymer and reduce their tendency to ball up into insoluble masses. Mechanical feed devices and eductors operated by flowing water have been described and are comercially used for this purpose. Sometimes such devices work well with cold water, but may give considerable difficulty when used with warm or hot water.
Certain high molecular weight, water-soluble polymers such as the various cellulose ethers, xanthan gum, guar gum and the like have been surface treated with crosslinking agents, such as glyoxal, to decrease the rate of hydration of these polymers in aqueous liquids. In this manner, the polymers are able to be dispersed before they start to hydrate (solubilize).
Concentrated suspensions of water-soluble polymers in inert organic liquids which do not appreciably swell the polymers recently have been introduced to the drilling industry. Such suspensions generally contain a high concentration of the water-soluble polymer, an organic suspending medium such as a hydrocarbon, a surfactant for enhancing the release of the polymer into an aqueous liquid and a suspending agent such as an organophilic clay. A formula and method for preparing a liquid hydroxyethylcellulose (HEC) suspension published by Union Carbide Corporation consists of 1.39% BENTONE 34 organophilic clay, 0.28% methanol, 42.5% HEC-25, and 2% TERGITOL NP-10 surfactant in a hydrocarbon (diesel fuel). A formula and method for preparing a liquid HEC suspension published by Hercules Incorporated consists of 37.0% NATROSOL 250-HHW (HEC), 40.1% of an ethyl hexanol premix containing 1% KLUCEL H hydroxypropyl cellulose, 21.1% ISOPAR M oil, and 1.8% BRIJ SP35 surfactant. A formula and method for preparing a liquid xanthan gum suspension published by Kelco Div., Merck & Co., Inc. consists of 53% mineral oil, 1 % EMEREST 2648 surfactant, 1% TRITON x-45 surfactant, 40% KOD85 xanthan gum biopolymer, 1% isopropyl alcohol, and 4% organophilic clay. Diesel fuel can be substituted for the mineral oil provided 7% organophilic clay is used in the liquid polymer composition.
These methods of suspending the water-soluble polymers suffer from various deficiencies including: incomplete suspension resulting in hard packing of the polymer on standing, hydration of the suspension on storage, poor dispersion of the polymer into aqueous liquids under conditions of low shear mixing and the like.
It would be desirable to provide a method of suspending water-soluble polymers prior to adxixture with an aqueous liquid which overcome at least some of the problems associated with the currently available suspensions.